This invention relates to a four-cycle outboard motor and more particularly to an improved oil pan arrangement for such outboard motors.
Because of environmental and other reasons, the more conventionally utilized two-cycle engines in outboard motors are being replaced by four-cycle engines. Many of the problems attendant with the design and construction of outboard motors become magnified when utilizing four-cycle engines.
Obviously, one of the main design criteria for an outboard motor is provide a compact yet efficient and high output system. This is one reason why two-cycle engines have been previously employed for these applications. The two-cycle engine, because of its firing of every rotation of the crank shaft tends to have a higher specific output then a like displacement four-cycle engine.
As noted above, however, certain factors are increasing the desire to utilize four-cycle engines for outboard motors. Thus, in addition to the normal problems of providing an effective exhaust system and good silencing, it is also necessary to incorporate an oil reservoir for the lubricating system of the four-cycle engine.
In order to provide a large oil reservoir and still a compact low center of gravity for the outboard motor, it is generally a practice to position the oil pan for the engine lubricating system on the underside of the exhaust guide. The exhaust guide is positioned at the upper end of the drive shaft housing and lower unit and supports the engine on its upper surface. The exhaust guide also attaches one or more exhaust pipes for delivering exhaust gases to the drive shaft housing for silencing an eventual discharge to the atmosphere.
When the oil pan for the engine is mounted in the drive shaft housing and lower unit, this presents certain problems in connection with servicing. That is, because of the recirculation of the lubricating oil, it should be changed at regular intervals.
Arrangements have been provided that permit the lubricant to be drained without removing the oil pan from the outboard motor. These generally employ arrangements wherein the oil pan has a portion that is positioned in proximity to the drive shaft housing. This oil pan portion has a drain plug that communicates with the exterior of the outboard motor through an opening in the drive shaft housing.
Because of the fact that the exhaust gases, particularly idle exhaust gas discharge must also be discharged to the atmosphere at a point high in the drive shaft housing, the idle exhaust gas discharge and the oil pan drain concepts compete with each other for space.
This has resulted in an arrangement wherein the drain for the oil pan is not positioned on the lower wall of the oil pan. Rather, there is a inclined rear wall and the drain is positioned in this inclined wall. This has several disadvantages.
First, because the drain is not in the lower wall, not all of the oil will be drained when it is changed. Furthermore, the inclined location makes it difficult to catch the drained oil and without some spillage.
These problems will be evident with the following description of the prior art type of constructions which are shown in partial detail in FIG. 1 which is a partial view of a prior art type of outboard motor, indicated generally by the reference numeral 31 and shows primarily the oil pan arrangement and the association of the oil pan with the exhaust system.
The conventional outboard motor 31 includes a power head, which is not shown but which extends above an exhaust guide 32 that is fixed and supported in a suitable manner across the upper end of a drive shaft housing unit, indicated generally by the reference numeral 33. This exhaust guide 32 has an exhaust passage 34 that communicates with the discharge end of an exhaust manifold of a four cycle internal combustion engine which is supported in the aforenoted power head and which is not illustrated.
An exhaust pipe 35 has a flanged portion 36 that is affixed to the underside of the exhaust guide 32 by threaded fasteners 37. The exhaust pipe 35 has an inlet end that is configured to be complementary to the exhaust guide exhaust passage 34 so as to collect the exhaust gases and deliver them downwardly to an expansion chamber 38 that is formed in the drive shaft housing lower unit 33.
The engine, which as has been noted is not shown, is of the four-cycle type. Therefore, there is provided an oil pan or oil reservoir 39 that is mounted on the underside of the exhaust guide 32 in a suitable manner and which contains lubricant for the engine.
This oil pan 39 is formed with an oil drain arrangement 41 that includes a drain plug 42 that is tapped into a threaded opening in an inclined lower wall 40 of the oil pan 39. A sealing gasket 43 surrounds the drain plug 42 and the drain plug is accessible through an access opening 44 formed in the drive shaft housing 33. This permits the lubricant to be drained from the oil pan 39 without its removal from the outboard motor 31. The drain plug 42 extends through an inner wall 45 of the drive shaft housing 33 and which is surrounded by a cowling portion 46.
However for several reasons including the exhaust arrangement to be described the wall 40 is not the lowermost wall of the oil pan 39 and thus it is difficult to insure that it will be fully drained. This is particularly true if servicing is done when the outboard motor is attached to a watercraft. Also the inclination of the wall 40 requires an inclined drain path which makes it difficult to insure that the oil will not run onto the exterior surfaces of the motor during draining.
It should be seen that the oil pan 39 is formed with an inner wall 47 that surrounds the exhaust pipe 35. The lower wall of the oil pan 39 terminates well above the lower end of the exhaust pipe 35. This means that when the outboard motor 31 is operating at idle or trolling condition, the end of the exhaust pipe 35 may be quite close to the water level. If misfiring occurs, either accidentally or intentionally to control the speed of the engine, negative pressure pulses may exist in the exhaust pipe 35. The water may then be drawn upwardly into the exhaust system when this occurs, obviously not a desirable condition.
The exhaust gases from the expansion chamber 38 are discharged to the atmosphere through a conventional underwater high-speed exhaust gas discharge. This may include a known type of through-the-hub underwater discharge.
Under low speed and low loads, however, the exhaust gases are delivered to the atmosphere through an above-the-water exhaust gas discharge. This is done because the back pressure would be too high to permit the discharge of the exhaust gases through the main exhaust system.
This idle discharge system includes a restricted passage 48 that is formed in the upper part of the exhaust pipe 35. The exhaust gases pass through this opening 48 and are deflected away from the oil pan wall 47 by a baffle 49. The exhaust gases then flow downwardly as indicated by the arrow 51 to an area between the outer surface of the oil pan 39 and across the inclined wall 40 and an inner surface wall 52 of the drive shaft housing 45. These exhaust gases then flow upwardly and through a restricted passageway 53 in the wall 52 as shown by the arrow 54. The exhaust gases then pass into an expansion chamber 55 formed by a further wall and which then can flow to the atmosphere through an idle discharge passage 56 formed in the drive shaft housing 33 in the direction of the arrow 57.
A water drain 58 is formed at the lower end of the expansion chamber 55 so that water that may be entrapped with the exhaust gases 10 drains back to the body of water in which the watercraft is operating.
The engine, which is not shown, has a water cooling system that includes a cooling jacket through which coolant is circulated by a water pump in a known manner. This coolant is then discharged at least in part to a cooling jacket 59 formed in the exhaust guide 32 around the exhaust passage 34. This water then fills a weir type device surrounding the oil pan 39 for its cooling and is discharged downwardly through a drain passage 61 for discharge through the lower unit in a known manner.